Alarm bolt

ABSTRACT

An alarm bolt is slidably mounted in aligned apertures through upstanding legs of a U-shaped bracket. A U-shaped spring having an inwardly extending protrusion on both upstanding arms is fastened to the bracket with the arms extending upwardly around opposite sides of the bolt. The protrusions on the arms of the spring engage and yieldably hold the bolt in its normal operating plane parallel to the door, but when sufficient lateral force is applied to the bolt, the arms will spread and allow the bolt to pivot upwardly. Upward pivoting of the bolt out of its normal operating plane is permitted by an oversized aperture in one of the bracket legs. When the end of the bolt pivots upwardly it engages and closes a pair of spaced contacts suspended closely over the bolt to complete a circuit to an alarm buzzer which signals the presence of the intruder. To shut off the buzzer, a restoring force must be applied from the inside of the locked door opposite in direction to the force applied by the intruder. A pair of diverging sloping lateral surfaces integral with the bolt registers with the spring when the bolt is slid open to restore the bolt to its normal sliding plane and open the contacts to silence the buzzer.

United States Patent [1 1 Bobrowski et al.

[ ALARM BOLT [75] Inventors: Louis G. Bobrowski, Berlin; Charles R. Suska, Roxbury, both of Conn.

[73] Assignee: The Stanley Works, New Britain,

Conn.

[22] Filed: Sept. 30, 1971 [21] Appl. No.: 185,308

Primary Examiner-John W. Caldwell Assistant Examiner-Scott F. Partridge Attorney-Granville M. Brumbaugh et al.

[ Aug. 28, 1973 [5 7] ABSTRACT An alarm bolt is slidably mounted in aligned apertures through upstanding legs of a U-shaped bracket. A U- shaped spring having an inwardly extending protrusion on both upstanding arms is fastened to the bracket with the arms extending upwardly around opposite sides of the bolt. The protrusions on the arms of the spring engage and yieldably hold the bolt in its normal operating plane parallel to the door, but when sufficient lateral force is applied to the bolt, the arms will spread and allow the bolt to pivot upwardly. Upward pivoting of the bolt out of its normal operating plane is permitted by an oversized aperture in one of the bracket legs. When the end of the bolt pivots upwardly it engages and closes a pair of spaced contacts suspended closely over the bolt to complete a circuit to an alann buzzer which signals the presence of the intruder. To shut off the buzzer, a restoring force must be applied from the inside of the locked door opposite in direction to the force applied by the intruder. A pair of diverging sloping lateral surfaces integral with the bolt registers with the spring when the bolt is slid open to restore the bolt to its normal sliding. plane and open the contacts to silence the buzzer.

' 12 Claims, 3 Drawing Figures ALARM BOLT This invention relates to alarm bolts, and more particularly to an alarm bolt which can be fastened to the inside surface of a door or the like.

With the increase in the crime rate over the last few years and the consequent decrease in law enforcement protection occasioned by the greater work load borne by the police, there has been an increasing consumer demand for security devices such as bolts and alarm systems which not only deny the intruder access to protected premises but also signal his presence to alert the police and to frighten him from further attempts to gain access to the premises.

Various forms of bolts and locks have been designed in attempting to fulfill this need. The protection afforded by bolts alone, however, is not sufficient, for although they may slow the intruders access to the building, eventually they can be broken or by-passed if the intruder has sufficient time, determination, and skill which is increasingly the case.

The other major deterrent to entrance by the intruder into the protected building is an alarm system. An alarm system by itself does not prevent entry but is intended to inhibit and terminate attempts thereat by announcing the fact of the intruders presence to the occupants and the police. Alarm systems that are within the means of most homeowners have proven ineffective because intruders have been able either to deactivate the alarm shortly after it is activated or to complete their crime and depart before the police could arrive.

The ideal system would appear to be a combination of a bolt and an alarm system. Such a system would deny access to the intruder while announcing his efforts to gain access. Typically, however, the available combinedbolt-alarm systems do not work concurrently: the alarm is not activated until the bolt is broken. Thus, the intruder has been able to work in silence until he gained access; only after access was gained would the alarm sound. The speedy intruder would thus have time to complete his crime and escape before arrival of the police. Moreover, these combined bolt and alarm systems are very expensive and financially beyond the means of all but the most wealthy home owners.

There have been proposals in the past for combining an alarm with a bolt or lock so that tampering with the bolt would cause an alarm to sound. These devices have not proven successful primarily because the alarm would stop sounding as soon as the pressure was removed from the bolt. Thus forewarned, the intruder could work in silence either to deactivate the alarm system or find another access into the protected building.

To overcome these defects, one solution was to arrange the alarm so that it would continue to sound even after the pressure against the bolt was removed. While this would initially appear to solve all outstanding problems, there remained the very practical difficulty of silencing the alarm: once activated, the alarm could be silenced only by disassembling the lock or bolt. This inconvenience is bearable when the alarm is activated by an intending intruder, for the inconvenience is slight compared to the security of the inhabitants of the protected building. However, the convenience is intolerable in cases in which the alarm is activated by innocent pressure against the door, for example, a bump by a milkman early in the morning or by the tenant of a neighboring apartment arriving home late at night. In

such circumstances it is desirable to be able to silence the alarm quickly without the necessity of disassembling the entire apparatus.

The need has thus existed for many years for an alarm bolt which will signal the intention of the intruder prior to his gaining entrance and which is easily silenced, but only from within.

SUMMARY OF THE INVENTION Accordingly, the present'invention provides a novel alarm bolt of simple, rugged, reliable and inexpensive construction for locking a door or the like and for sounding an alarm when forced entry is attempted before entry is gained, to give the occupants time to summon help, which alarm can easily be silenced, but only from within.

The alarm bolt has a bolt mounted in a bracket for normal sliding movement in a path parallel to the door to engage a strike. The bolt is also pivotally mounted in the same bracket for pivoting out of its normal sliding path when unauthorized entry is attempted. When the bolt pivots out of the path, it closes a pair of contacts which completes an electric circuit to an alarm device which will commence to sound. A biasing spring normally holds the ,bolt in its nonnal operating path but, when sufficient force is applied, the biasing spring will yield and allow the bolt to pivot. The spring then functions as a detent to catchthe bolt and hold it in its pivoted position thereby causing the alarm to continue to sound. To silence the alarm it is merely necessary to slide the bolt to its opened position which will make the position of the spring-bolt system unstable and the spring will return the bolt back to its normal path.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Looking now at the drawings wherein like reference characters designate identical or corresponding parts, and more particularly to FIGS. 1 and 2 thereof, an alarm bolt according to the present invention is shown having a bolt 10 slidably mounted in a bracket 12 in position to engage a strike 14 mounted on a jam 16 which cooperates with a door 18 on which the bolt is to be mounted. To lock the door in its closed position, it is merely necessary to slide the bolt 10 to the left into an aperture 20 formed in the strike 14 thereby preventing the door from pivoting clockwise about its hinge (not seen) to the right of the door as viewed in FIG. 2.

The bracket 12 in which the bolt 10 slides in axial translation to engage the strike 14 is a shallow U- shaped member having a pair of upstanding legs 22 and 24 joined by a flat base 23 on which is formed a laterally extending bearing ridge 25 which provides bearing support for axial translation of the bolt and also acts as a fulcrum during pivotal movement of the bolt 10 as will be explained later. The legs 22 and 24 have apertures 26 and 28 respectively formed therein which are for the purpose of guiding the axial translation of the bolt 10. The size of the aperture 26 in its vertical dimension, that is, normal to the plane of the door, is just sufficient to permit the bolt to slide without interference; the vertical dimension of the aperture 28 is enlarged to permit a certain degree of vertical movement of the rear end of the bolt for a purpose which will appear presently. The dimension of the apertures 26 and 28 in the lateral direction, that is, parallel to the plane of the door and perpendicular to the axis of the bolt, is just sufficient to permit passage of bolt 10 without interference with the sides of the apertures. The top of the aperture 28 is laterally enlarged as best seen in FIG. 3 and forms a pair of shoulders 29 at the junction of the narrow and the enlarged portion of the aperture 28.

An intermediate member 30, formed of a bar of a synthetic resin, such as Lexan, is rigidly fastened to the bolt 10 by conventional fasteners such as rivets, or, as illustrated, by pressing the member 30 onto two serrated studs 32 integral with the bolt 10. The intermediate member 30 has a first section 31 at the forward end thereof, that is, the end closest to the leg 22, on which a knob 34 (see only in Fig. 1) is formed, by means of which the bolt 10 may be axially slid in bracket 12 for locking and unlocking the door. Immediately rearward, or to the right as viewed in FIG. 2, of its connection to knob 34, the bar is thickened and widened at 36 to form a raised plateau having lateral sloping sides which diverge vertically downward or toward the door so that the lateral width of this second or plateau section 36 of the intermediate member 30 is wider at the inside or bottom face than at the outside or top face. The rear, or third section 38, of the intermediate member 30 constitutes approximately one half the length of the bar and is of the same height as the first section 31 and as wide as the widest part of the plateau section 36. A pair of notches 40 are formed in the bottom lateral edges of the third section 38 and extend axially therealong rearwardly from the plateau section 36, ending slightly forward of the end of the intermediate member 30. The notches 40 extend vertically approximately one half the thickness of the bar, and are approximately equal in lateral and vertical dimension. The axial ends 41 of the notches 40 engage the shoulders 29 of the aperture 28 to limit the axial travel of the bolt 10. The sloping plateau sides and the sides of the third section 38 cooperate with a spring 42 to function as a biasing, holding and automatic restoring arrangement for the bolt 10 as will appear presently.

The U-shaped spring 42 is fastened to the bracket 12 adjacent the rear leg 24 by conventional means such as a rivet 44. The upstanding arms 46 of spring 42 extend upwardly around both lateral sides of the bolt 10. A longitudinal protrusion 48 is formed horizontally on each of the legs 46 and extends inwardly toward the bolt 10. Protrusion 48 may consist of a V-shaped bend in the leg 46 as best illustrated in FIG. 3, or they may be a welding bead or other thickening of legs 46 at that point. The height at which protrusions 48 are formed on legs 46 corresponds to the height of third section 38 above the base 23 of the bracket 12 so that protrusions 48 project inwardly over the top of the intermediate member 30 and bear thereagainst. Legs 46 of spring 42 thus exert a downward biasing force on the intermediate member 30 and, therethrough, on bolt 10 to prevent vertical movement thereof out of its normal operating path parallel to the door. However, should a vertical force be applied to bolt 10 sufficient to overcome the biasing force of the spring arms 46 and pivot the bolt 10 out vof its normal operating path, the legs 46 will momentarily spread and the bolt 10 will pivot up and abut the inside top edge of aperture 28. At this position of bolt 10, the protrusions 48 of the legs 46 will bear against the lateral sides of the third section 38 above the notches 40, or just barely engage the top outside comers of notches 40. Spring 42 thus acts as a resilient biasing means yieldably holding bolt 10 in the plane of its normal operating path, and also as a resilient grasping and holding means, operative to yieldably hold bolt 10 in its angularly displaced position after bolt 10 has been so displaced. A third function of the spring 42 in combination with the intermediate member 30, that of automatic restoration of the bolt 10 to the plane of its normal operating path, will be explained in the description of operation of this preferred embodiment.

A suitable case may be fastened to the alarm bolt by screws extending into upstanding receptacles 50. A snap-in removable grille may be received by the case to facilitate access to the arm bolt and enable transmission sound waves from the alarm. The case and grille may be of the design shown in copending US. design application Ser. No. 178,852, filed Sept. 8, 1971, for Alarm Unit, assigned to the assignee of this invention.

With reference again to FIG. 1, the operation of the alarm bolt is as follows. The vertical risepermitted the bolt 10 is limited by engagement of the top of the third section of the intermediate member 30 against the top of the aperture 28, therefore the protrusions 48 do not fully enter the notches 40 but merely bear against the lateral sides of the third section 38, or engage the top outside comers of notches 40. The door 18 on which the alarm bolt is mounted is closed against the jam 16 so that the bolt 10 is axially aligned with the aperture 20 through the strike 14. The knob 34 is grasped by the hand and moved to the left to cause the bolt 10 to slide axially through the apertures 26 and 28, over the bearing ridge 25, and into the aperture 20 in the strike 14 to lock the door in closed position.

If an intruder attemps to force entry by prying the door open, the force F of this push will be transmitted to the bolt 10 through the bearing ridge 25 and the door will move in an incremental distance until bolt 10 engages the inside top edge of the aperture 20. Strike 14 will then exert a resisting force R against the top surface of the bolt 10 to restrain further opening of the door. The force R and F produce a counterclockwise movement which tends to pivot bolt 10 about the bearing ridge 25, which now acts as a fulcrum. If the force F against the door 18 is great enough, the biasing force exerted by the spring 42 against the top of the intermediate member 30 will be overcome and spring arms 46 will spread to pennit bolt 10 to pivot in a counterclockwise direction about bearing ridge 25. Only a short angular displacement is permitted, however, because aperture 28 through rear leg 24 is large enough to permit the bolt 10 to rotate only 1 or 2 out of the plane of its normal operating path parallel to the door 18 and thereafter prevents further rotation.

When the bolt is pivoted out of the plane of its normal operating path parallel to the door, the third section 38 of the intennediate member 30 passes upward into registry with the longitudinal protrusions 48 which then bear against the lateral sides of the third section 38 and thereby prevent bolt from swinging freely back into its plane parallel to the door. To return the bolt to its normal plane parallel to the door, it is necessary to exert a force on the rear end of the bolt normal to and toward the door, or a force on the front end of the bolt 10 normal to and away from the jam l6 suffi cient to overcome the frictional force of the protrusions 48 bearing against the lateral sides of the third section 38. Neither force can be exerted by the intending intruder because he would have to be inside to exert a force on the rear end of the bolt, and pulling the door closed from the outside does not cause the front end of bolt 10 to engage the jam or the bottom edge of the aperture 20, there being sufficient clearance left in those dimensions for just this reason.

These forces may be exerted by the occupant of the protected building, but a more simple and more convenient means to return bolt 10 to the plane of its normal path would be desirable and is provided by the sloping lateral sides of the plateau section 36. To return bolt 10 to its normal operating plane, it is merely necessary to grasp knob 34 and move it to the right,thereby bringing the sloping sides of plateau 36 into registry with the protrusions 48 on the legs 46 which now bear against the sloping sides of plateau section 36.

The forces exerted through the protrusions 48 by the spring legs 46 on the sloping sides of the plateau section 36 act only in a direction normal to the plane of the sloping sides against which the spring legs act. The components of the forces exerted parallel to the plane of the door cancel since the forces exerted by the two spring arms are equal. The total resultant force exerted on the bolt 10 by the spring arms, then is a force normal to and toward the door which causes the bolt 10 to pivot smoothly about the bearing ridge 25 into the plane of its normal operating path. At this point, the protrusions 48 of the spring 42 extend over and bear against the top edges of the plateau section 30 to exert abiasing force tending to hold bolt 10 in its normal operating path thereby preventing inadvertent pivoting to its angularly displaced position. The sytem formed by the cooperating spring 42 and intermediate member 30 is thus a complex bistable-monostable system which gives the bolt 10 two stable angular positions in its locked configuration: a first position for normal operation in which the bolt 10 may be shifted axially between locked and unlocked configuration, and a second position, angularly displaced from the first position in which the alarm circuit is closed by a forced entry. In the unlocked configuration, the bolt has only one stable angular position namely the first or normal operating position, which explains the automatic restoring feature of the bolt. A stable" position is defined for use herein as one in which the bolt 10 will remain until application of a significant force, i.e., a pound.

Looking again at FIG. 1, the assembly illustrated in FIGS. 2 and 3 is contained in a housing 54 which holds an alarm device such as a siren or buzzer 56, a battery 58 for energizing the buzzer 56, and a pair of normally open, closely spaced electrical contacts 60. Contacts 60 are in series in the battery-buzzer circuit and when closed they complete the circuit. Contacts 60 are disposed immediately above intermediate member 30 so that when bolt 10 is pivoted as described above, intermediate member 30 will engage the nearer of contacts 60 and push it into contact with the other of contacts 60 thereby completing the electric circuit and energizing the buzzer which emits an ear-splitting alarm calculated to alert the occupants of the building and frighten the discovered burglar into hasty flight. Since bolt 10 is held in its angularly displaced position by engagement of protrusions 48 with the sides of the third section 38 the buzzer continues to sound until bolt 10 is returned to its nonnal operating plane by action of the occupant of the building if he desires to silence the buzzer. Otherwise the buzzer will continue to sound for the life of the battery.

Should the occupant desire to test the buzzer to make sure it works, he merely need grasp the door handle from the inside when the door is locked and give a sharp pull; this will actuate the buzzer. Satisfied that it works, the owner then will quickly open the bolt by sliding the knob, to theright to silence the buzzer. The owner therefore has the option of testing the alarm if he wants to, but is not inconvenienced by an automatic test when he has no desire to test or when he wants to enter and leave his building quietly.

Thus, there is provided a simple, rugged, reliable and inexpensive alarm boltthat will sound a continuous alarm as soon as forced entry is first attempted. The alarm may easily be silenced by the occupant, if he desires, but only from the inside. To enter the building, the intruder must work to break the sturdy bolt with din of the alarm sounding in his cars, a prospect which would deter virtually all burglars. The alarm bolt is so inexpensive and easily installed that protection for every door in the house is now easily obtainable.

The present invention may be practiced by numerous modifications and variations of the above-described preferred embodiment or best mode. For example, the spring system formed of the spring 42 and the intermediate member 30 may be replaced with a bistable spring system such as a compression or toggle spring whose line of force is shortest at the midposition between the two angular positions of the bolt 10, and which operates through a cam to return the bolt 10 to its first angular position when shifted to unlocked configuration. It is, therefore, expressly to be understood that the invention, defined in the appended claims may be practiced otherwise than as specifically described herein.

I claim: 1. An alarm bolt, comprising: a bolt; mounting means for mounting said bolt on a door for normal sliding movement along a path into a strike mounted on a jamb to which the door is to be bolted, said mounting means also pivotally mounting said bolt for pivotal movement out of said path;

resilient means for biasing said bolt against said pivotal movement out of said path and, after said bolt has pivoted a predetermined angular displacement against said resilient means out of said path, for releasably holding said bolt in said angularly displaced position;

a normally open electrical circuit including means associated with said bolt for completing said electrical circuit upon said pivotal movement of said bolt out of said path; and alarm means connected in said electrical circuit for signaling when said circuit is complete. 2. The alarm bolt defined in claim 1, wherein said mounting means comprises:

guide means for guiding said bolt in axial translation in a plane parallel to the door; and bearing means for pivotally supporting said bolt during said pivotal movement thereof, and also for providing bearing support for said bolt during axial translation thereof. 7 3. The alarm bolt defined in claim 1, wherein said mounting means comprises:

a metal bracket having a base and connected thereto a pair of spaced upstanding legs;

means defining an aperture in each leg for receiving said bolt and guiding axial translation thereof;

bearing means formed on said base for providing fulcrum support for said bolt during pivotal movement thereof and also for providing bearing support for said bolt during axial translation thereof.

4. The alarm bolt defined in claim 1, wherein said resilient means comprises:

resilient spring means for holding said bolt in said path and operative to release said bolt for pivoting out of said plane upon application of a predetermined force thereagainst, and also for holding said bolt in said angularly displaced position until application of a predetermined force sufficient to restore said bolt to said path, said resilient spring means comprising a pair of arms bracketing said bolt, each of said arms having a protrusion formed thereon extending inwardly toward and operatively engaging said bolt.

5. The alarm bolt defined in claim 1, wherein said resilient means comprises:

bistable spring means having a first stable position holding said bolt in a first angular position parallel to said door, and operative to yield to a predetermined force and allow said bolt to pivot out of said first angular position into a second angular position angularly displaced from-said first angular position, whereat said spring means is in a second stable position releasably holding said bolt in said second angular position until application of a predetermined force sufficient to restore said bolt to said plane.

6. The alarm bolt defined in claim 5, wherein:

said bistable spring means comprises a pair of spring arms bracketing said bolt, at least one of said arms having a protrusion formed thereon and extending inwardly toward and operatively engaging said bolt; and said mounting means comprises a metal bracket having a base and connected thereto a pair of spaced upstanding legs, and means defining an aperture in each leg for receiving said bolt and guiding said axial translation thereof; one of said apertures being sufficiently enlarged to permit angular displacement of said bolt from said first angular position to said second angular position, and bearing means formed on said base for providing fulcrum support for said bolt during pivotal movement thereof and also for providing bearing for said bolt during axial translation thereof. 7. The alarm bolt defined in claim 5, further comprising intermediate means connected to said bolt, and cooperating with said mounting means andsaid resilient means for:

bearing said resilient means in said second angular position of said bolt; 7 limiting said axial translation of said bolt; pivoting said bolt to said normal operating plane when said bolt is axially translated away from engagement with said strike; and

providing a hand grip for manual manipulation of said bolt.

8. The alarm bolt defined in claim 7, wherein said interrnediate member comprises:

an elongate bar;

a knob connected to said bar for manual manipulation of said bolt;

means formed in opposite lateral sides of said bar defining a pair of longitudinal notches for cooperating with one of said upstanding legs for guiding and limiting axial translation of said bolt; and raised plateau extending above the top surface of said bar and having sloping sides tapering downward from the top of said plateau to the back surface of said bar, said plateau being formed immediately adjacent to the ends of said notches, whereby axial translation of said bolt when said protrusion is engaged with one of the lateral sides of said intermediate member will carry one of the sloping plateau sides into registry with said protrusion which, bearing against said sloping side, will cause said bolt to pivot inwardly.

9. The alarm bolt defined in claim 4, further comprising a monostable-bistable spring system formed by the cooperation of said resilient spring means and an intermediate member connected to said bolt and through which forces may be exerted on said bolt, said intermediate member including an elongate bar, a knob connected to a first section of said bar for manual manipulation of said bolt, a third section of said bar having perpendicular lateral sides, a second section of said bar having sloping sides tapering backward from the top of said second section to the back surface of said bar, said second section being formed immediately adjacent to the third section of said bar, said protrusions bearing against the top of said third section to bias said bolt in its normal operating path, but said spring arms will yield and spread upon application of a predetermined force to allow said bolt to pivot upwardly out of its normal operating path into an angularly displaced position whereat the lateral sides of said third section will be engaged by said protrusions and said bolt will be held in said angularly displaced position until application of a return force of predetermined magnitude, whereby axial translation of said bolt when said protrusions are engaged with said perpendicular lateral sides of said third sections will carry said sloping sides of said second section into registry with said protrusions which, bearing against said sloping sides, will cause said bolt to pivot inwardly, wherein said resilient spring means cooperates with said second section to form a monostable system and with said third section to form a bistable system.

10. An alarm bolt, comprising:

a bolt;

a bracket for mounting said bolt on a door for normal sliding movement along a path into a strike mounted on a jamb to which the door is to be bolted, said bracket also pivotally mounting said bolt for pivotal movement out of said path;

a spring including a spring arm having a projection surface means on said bolt which, in the fully locked position of said bolt, forms with said spring a bistable system such that said bolt when in the plane of its normal sliding path will be biased by said spring to remain in the plane of said normal sliding movement path and, after said bolt has been moved against said spring to an angularly displaced position out of the plane of said normal sliding movement path, said bolt will be releasably gripped and held by said spring in said displaced position;

said surface means on said bolt, in a partially unlocked position of said bolt, forming with said spring a monostable system which is stable with the bolt in its normal sliding path only, such that when said bolt is in said partially unlocked position, said bolt will be biased by said spring to the plane of said normal sliding movement path.

bearing said resilient means in said angularly displaced position of said bolt;

limiting said sliding movement of said bolt;

pivoting said bolt to the plane of said normal sliding path when said bolt is slid to said partially unlocked position; and

providing a hand grip for manual manipulation of said bolt.

12. The alarm bolt defined in claim 11, wherein said 10 intermediate member comprises:

an elongate bar;

a knob connected to said bar for manual manipulation of said bolt;

means formed in opposite lateral sides of said bar defining a pair of longitudinal notches for cooperating with one of said upstanding legs for guiding and limiting normal sliding movement of said bolt; and

a raised plateau extending above the top surface of said bar and having sloping sides tapering downward from the top of said plateau to the back surface of said bar, said plateau being formed immediately adjacent to the ends of said notches, whereby normal sliding movement of said bolt when said protrusion is engaged with one of the lateral sides of said intermediate member will carry one of the sloping plateau sides into registry with said protrusion which, bearing against said sloping side, will cause said bolt to pivot inwardly.

11. The alarm bolt defined in claim 10, wherein said surface means comprises intermediate means connected to said bolt, and cooperating with said mounting means and said resilient means for: 

1. An alarm bolt, comprising: a bolt; mounting means for mounting said bolt on a door for normal sliding movement along a path into a strike mounted on a jamb to which the door is to be bolted, said mounting means also pivotally mounting said bolt for pivotal movement out of said path; resilient means for biasing said bolt against said pivotal movement out of said path and, after said bolt has pivoted a predetermined angular displacement against said resilient means out of said path, for releasably holding said bolt in said angularly displaced position; a normally open electrical circuit including means associated with said bolt for completing said electrical circuit upon said pivotal movement of said bolt out of said path; and alarm means connected in said electrical circuit for signaling when said circuit is complete.
 2. The alarm bolt defined in claim 1, wherein said mounting means comprises: guide means for guiding said bolt in axial translation in a plane parallel to the door; and bearing means for pivotally supporting said bolt during said pivotal movement thereof, and also for providing bearing support for said bolt during axial translation thereof.
 3. The alarm bolt defined in claim 1, wherein said mounting means comprises: a metal bracket having a base and connected thereto a pair of spaced upstanding legs; means defining an aperture in each leg for receiving said bolt and guiding axial translation thereof; bearing means formed on said base for providing fulcrum support for said bolt during pivotal movement thereof and also for providing bearing support for said bolt during axial translation thereof.
 4. The alarm bolt defined in claim 1, wherein said resilient means comprises: resilient spring means for holding said bolt in said path and operative to release said bolt for pivoting out of said plane upon application of a predetermined force thereagainst, and also for holding said bolt in said angularly displaced position until application of a predeteRmined force sufficient to restore said bolt to said path, said resilient spring means comprising a pair of arms bracketing said bolt, each of said arms having a protrusion formed thereon extending inwardly toward and operatively engaging said bolt.
 5. The alarm bolt defined in claim 1, wherein said resilient means comprises: bistable spring means having a first stable position holding said bolt in a first angular position parallel to said door, and operative to yield to a predetermined force and allow said bolt to pivot out of said first angular position into a second angular position angularly displaced from said first angular position, whereat said spring means is in a second stable position releasably holding said bolt in said second angular position until application of a predetermined force sufficient to restore said bolt to said plane.
 6. The alarm bolt defined in claim 5, wherein: said bistable spring means comprises a pair of spring arms bracketing said bolt, at least one of said arms having a protrusion formed thereon and extending inwardly toward and operatively engaging said bolt; and said mounting means comprises a metal bracket having a base and connected thereto a pair of spaced upstanding legs, and means defining an aperture in each leg for receiving said bolt and guiding said axial translation thereof; one of said apertures being sufficiently enlarged to permit angular displacement of said bolt from said first angular position to said second angular position, and bearing means formed on said base for providing fulcrum support for said bolt during pivotal movement thereof and also for providing bearing for said bolt during axial translation thereof.
 7. The alarm bolt defined in claim 5, further comprising intermediate means connected to said bolt, and cooperating with said mounting means and said resilient means for: bearing said resilient means in said second angular position of said bolt; limiting said axial translation of said bolt; pivoting said bolt to said normal operating plane when said bolt is axially translated away from engagement with said strike; and providing a hand grip for manual manipulation of said bolt.
 8. The alarm bolt defined in claim 7, wherein said intermediate member comprises: an elongate bar; a knob connected to said bar for manual manipulation of said bolt; means formed in opposite lateral sides of said bar defining a pair of longitudinal notches for cooperating with one of said upstanding legs for guiding and limiting axial translation of said bolt; and a raised plateau extending above the top surface of said bar and having sloping sides tapering downward from the top of said plateau to the back surface of said bar, said plateau being formed immediately adjacent to the ends of said notches, whereby axial translation of said bolt when said protrusion is engaged with one of the lateral sides of said intermediate member will carry one of the sloping plateau sides into registry with said protrusion which, bearing against said sloping side, will cause said bolt to pivot inwardly.
 9. The alarm bolt defined in claim 4, further comprising a monostable-bistable spring system formed by the cooperation of said resilient spring means and an intermediate member connected to said bolt and through which forces may be exerted on said bolt, said intermediate member including an elongate bar, a knob connected to a first section of said bar for manual manipulation of said bolt, a third section of said bar having perpendicular lateral sides, a second section of said bar having sloping sides tapering backward from the top of said second section to the back surface of said bar, said second section being formed immediately adjacent to the third section of said bar, said protrusions bearing against the top of said third section to bias said bolt in its normal operating path, but said spring arms will yield and spread upon application of a predetermined force to allow said bolt to pivOt upwardly out of its normal operating path into an angularly displaced position whereat the lateral sides of said third section will be engaged by said protrusions and said bolt will be held in said angularly displaced position until application of a return force of predetermined magnitude, whereby axial translation of said bolt when said protrusions are engaged with said perpendicular lateral sides of said third sections will carry said sloping sides of said second section into registry with said protrusions which, bearing against said sloping sides, will cause said bolt to pivot inwardly, wherein said resilient spring means cooperates with said second section to form a monostable system and with said third section to form a bistable system.
 10. An alarm bolt, comprising: a bolt; a bracket for mounting said bolt on a door for normal sliding movement along a path into a strike mounted on a jamb to which the door is to be bolted, said bracket also pivotally mounting said bolt for pivotal movement out of said path; a spring including a spring arm having a projection thereon extending toward said bolt, said arm disposed adjacent said bolt with said projection bearing against said bolt on an edge thereof which moves in a single plane during both pivotal and sliding movement of said bolt; surface means on said bolt which, in the fully locked position of said bolt, forms with said spring a bistable system such that said bolt when in the plane of its normal sliding path will be biased by said spring to remain in the plane of said normal sliding movement path and, after said bolt has been moved against said spring to an angularly displaced position out of the plane of said normal sliding movement path, said bolt will be releasably gripped and held by said spring in said displaced position; said surface means on said bolt, in a partially unlocked position of said bolt, forming with said spring a monostable system which is stable with the bolt in its normal sliding path only, such that when said bolt is in said partially unlocked position, said bolt will be biased by said spring to the plane of said normal sliding movement path.
 11. The alarm bolt defined in claim 10, wherein said surface means comprises intermediate means connected to said bolt, and cooperating with said mounting means and said resilient means for: bearing said resilient means in said angularly displaced position of said bolt; limiting said sliding movement of said bolt; pivoting said bolt to the plane of said normal sliding path when said bolt is slid to said partially unlocked position; and providing a hand grip for manual manipulation of said bolt.
 12. The alarm bolt defined in claim 11, wherein said intermediate member comprises: an elongate bar; a knob connected to said bar for manual manipulation of said bolt; means formed in opposite lateral sides of said bar defining a pair of longitudinal notches for cooperating with one of said upstanding legs for guiding and limiting normal sliding movement of said bolt; and a raised plateau extending above the top surface of said bar and having sloping sides tapering downward from the top of said plateau to the back surface of said bar, said plateau being formed immediately adjacent to the ends of said notches, whereby normal sliding movement of said bolt when said protrusion is engaged with one of the lateral sides of said intermediate member will carry one of the sloping plateau sides into registry with said protrusion which, bearing against said sloping side, will cause said bolt to pivot inwardly. 